The invention relates to fuel injectors for internal combustion engines, generally, and to heated tip fuel injectors, specifically. More specifically, this invention relates to a method and apparatus for controlling heated tip fuel injectors.
Fuel injectors are widely used for metering fuel into the intake manifold or cylinders of automotive engines. Fuel injectors typically comprise a housing containing a volume of pressurized fuel, a fuel inlet portion, a nozzle portion containing a needle valve, and an electromagnetic solenoid or other mechanism for actuating the needle valve. When the needle valve is actuated, the pressurized fuel sprays out through an orifice in the valve seat and into the engine.
In order to reduce emissions, it is desirable to have the fuel vaporize as it sprays out of the injector orifice. However, during cold starting conditions, fuel vaporization can be difficult to achieve. For this reason, cold starts account for a large proportion of engine emissions.
The use of fuel injector heaters has been proposed to overcome this problem. Fuel injector heaters may typically take the form of external heater jackets surrounding the injector. Preheating fuel during cold start conditions is known to reduce emissions caused by incomplete fuel vaporization during cold starts.
However, because the heating element of heated injectors typically consumes a significant amount of current during start-up, a voltage drop often occurs across the energy source (e.g., a battery) and across the internal resistance of the wiring and connectors in the fuel system wiring harness. As a result, the voltage available to actuate the fuel injector coil may be diminished, which can negatively influence the dynamic flow of the fuel injector. The present invention minimizes this undesirable voltage drop across the fuel injector coils, thereby ensuring full voltage is present to actuate the injectors and minimizing the effect of the heating elements on the dynamic flow of the injectors.
A method of measuring the temperature of fuel inside a fuel injector is provided. The method includes positioning a first resistive element having a resistance that varies with temperature proximal a fuel injector; electrically connecting a second resistive element having a certain resistance in series with the first resistive element at a node to form a resistor-divider network; and applying a known voltage across the resistor-divider network while measuring the voltage present at the node. The measured voltage corresponds to the temperature of the fuel within the fuel injector.
A method of controlling the temperature of fuel inside a fuel injector is also provided. The method includes positioning a first resistive element having a resistance that varies with temperature proximal a fuel injector; electrically connecting a second resistive element having a certain resistance in series with the first resistive element at a node to form a resistor-divider network; applying a known voltage across the resistor-divider network while measuring the voltage present at the node, the measured voltage corresponding to the temperature of the fuel within the fuel injector; comparing the voltage corresponding to the temperature of the fuel within the fuel injector with a predetermined value; and selectively energizing the first resistive element to heat the fuel within the fuel injector if the temperature corresponding to the measured voltage is less than the predetermined value.
A circuit for measuring the temperature of fuel inside a fuel injector is also provided. The circuit includes a first resistive element having a resistance that varies with temperature positioned proximal the fuel within a fuel injector. A second resistive element having a certain resistance placed in series with the first resistive element and electrically connected at a node to form a resistor-divider network. Applying a known voltage across the resistor-divider network generates a voltage at the node corresponding to the temperature of the fuel within the fuel injector.